This application claims the priority of International Application No. PCT/DE2007/001393, filed Aug. 4, 2007, and German Patent Document No. 10 2006 037 952.7, filed Aug. 12, 2006, the disclosures of which are expressly incorporated by reference herein.
The invention relates to a method for monitoring a production process with regard to quality.
The quality of components that are manufactured with the aid of a production process influences to a great degree the performance characteristics of the components. This applies particularly to highly stressed components of a gas turbine aircraft engine. In this connection, the quality of the components relates especially to the dimensional stability, the static and dynamic strength as well as to the surface quality of the components. It is possible only with great effort to test the quality of manufactured components in a non-destructive manner. As a result, methods for monitoring a production process that make it possible to determine the quality of the manufactured components are of interest.
Methods for monitoring a production process with regard to quality are known from practice in which signal curves of parameters of the production process are recorded using measuring techniques, wherein several signal curves that are recorded using measuring techniques, which can be allocated to a correct and therefore qualitatively high-value production sequence, are statistically analyzed in order to make target curves available for the signal curves that can be recorded using measuring techniques. To monitor a production process with regard to quality, actual curves of the signal curves that have been recorded using measuring techniques are compared with the target curves determined in advance for same, wherein a qualitatively poor production process is determined if the actual curves deviate from the target curves by more than a defined extent. According to the prior art, several actually measured signal curves of correct or qualitatively good production sequences are accordingly required to make the target curves available for the signal curves that can be recorded using measuring techniques in order to determine herefrom the target curves with the aid of stochastic analyses, i.e., by notification about the measurements that are therewith significant. However, if components are supposed to be manufactured in small lot sizes, the procedure for monitoring a production process with regard to quality that is known from practice is unsuitable.
Starting herefrom, the present invention is based on the objective of creating a method for monitoring a production process with regard to quality, which also makes monitoring in the case of small lot sizes possible.
The inventive method comprises at least the following steps: a) breaking down the production process into a sequence of individual steps, defined by a sequence of control commands for a production program for carrying out the production process on a machine tool; b) generating at least one signal template per individual step of the production process from the control commands for the individual steps, each signal template corresponding to a theoretical signal curve for a parameter which may be measured upon executing the production process; c) measurement of a signal curve for at least one parameter per individual step during the execution; d) comparison of the or each measured signal curve with the respective arithmetically generated signal template, wherein a qualitatively poor production process is determined if the measured signal curve deviates from the signal template by more than a given tolerance.
In terms of the inventive method, it is provided that the production process being monitored with respect to its quality be subdivided into a sequence of individual steps, wherein at least one signal template is arithmetically generated for each individual step from the control commands of the individual steps.
The signal templates provide target curves for signal curves of parameters of the production process, wherein, according to the invention, these signal templates are theoretically, arithmetically determined target curves and not, as in the prior art, target curves generated from real signal curves via statistical analyses. The advantage of this is that the inventive method may also be used for monitoring a production process with regard to quality if components with relatively small lot sizes are supposed to be manufactured with the production process being monitored.
The tolerance of each signal template is preferably defined by an upper limit and lower limit enveloping the theoretic signal curve, wherein the upper limit and lower limit along with the signal template are generated from the control commands of the individual steps.
According to an advantageous further development of the invention, signal templates as well as preferably corresponding upper limits and lower limits, which can be detected without additional sensors on the machine tool, are generated for these types of parameters.
Preferred further developments of the invention are disclosed in the following description. Without being limited hereto, exemplary embodiments of the invention are explained on the basis of the drawing.